Photographic emulsions sensitized with salts of metals of group viii of the periodicarrangement of the elements



ratenreu Aug. or, man

PHOTOGRAPHIC EMULSIONS SENSITIZED WITH SALTS OF METALS OF GROUP VIII OF THE PERIODIC ARRANGEMENT OF THE v ELEMENTS William F. Smith and Adrian P. H. Trivelli, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application July 15, 1946, Serial No. 683,772

19 Claims.

Thi invention relates to sensitized photographic emulsions and to a process for preparing the same.

There have been a number of methods proposed for enhancing the sensitivity of photographic silver halide emulsions other than the methods of optical or spectral sensitization which involve the incorporation of certain dyes in the emulsions. Many of these prior methods of enhancing sensitivity other than the methods of optical or spectral sensitization leave much to be desired because the increase of sensitivity is actually very small, or the increase of sensitivity is accompanied by excessive fog and/or excessively poor keeping qualities of the sensitized emulsions.

We have now found a method of enhancing the sgnflziy ity of photographic silver halide emulsions wherein the speed increases are very substantial, yet fog and keeping qualities, while affected to some extent, are not excessive considering the magnitude of the increases in speed obtained.

It is accordingly an object of our invention to provide new sensitized photographic silver halide emulsions. A further object is to provide a p ,ess for preparing such emulsions. will become apparent hereinafter.

Other objects In accordance with our invention, we incorporate in a photographic silver halide emulsion at least one water soluble metal compound wherein the metal is a metal selected from the group consisting of metals in group VIII of the periodic arrangement of the elements having an atomic weight greater than 100. Exemplary of such soluble metal compounds are: the compound which are represented by the following general formula:

RzMXe wherein R represents a hydrogen atom, an alkali metal atom or an ammonium radical, M represents a metal atom selected from group VIII of the periodic arrangement of the elements having an atomic weight greater than 100, i. e. "ruthenium, rhodium, palladium, osmium, iridium and platinum, and X represents a halogen atom, e. g. a chlorine or bromine atom. Still other metal compounds which we employ in practicing our invention are those which are represented by the following general formula:

wherein R represents a hydrogen atom, an alkali metal atom or an ammonium radical, M represents a palladium or a platinum atom, and X represents a halogen atom. Among the metal compounds set forth above are ammonium and potassium chl-oropalladate, ammonium, sodium and potassium chloroplatinate, ammonium, potassium and sodium bromoplatinate, ammonium chlororhodate, ammonium chlororuthen'ate, ammonium chlor-oiridate, ammonium, potassium and sodium chl-oroplatinite, ammonium, potassium and sodium chloropalladite, etc.

Our invention is directed primarily to developing-out silver halide emulsions in which the silver halide is predominately silver bromide, i. e. silver halideemulsions in which the silver halide is wholly silver bromide and silver bromide emulsions containin smaller amounts of silver chloride or silver iodide or both. However, emulsions in which the silver halide is wholly or predominately silver chloride are included in our invention. 1

The metal compounds are employed in an amount below that which produces any substantial fog inhibition. Photographic emulsions containing these metal compounds in fog inhibiting amounts are described in our copending application Serial No. 613,709, filed August 30, 1945, now abandoned. In practicing the instant invention,

we employ a quantity of the metal compound equivalent to from about 0.8 to somewhat less than 39.4 mg. for each g. of silver in the emulsion. Advantageously the quantity is from about 0.8 to about 19.7 mg..for each 100 g. of silver. This quantity is'sm aller thanthe quantity employed to inhibit fog in our aforesaid copending application. The metal compounds can be added to the emulsions at any stage of the preparation of the emulsions, i. e. before or during precipitation of the silver halides, before or during the first digestion (ripening) of the emulsion, before or during the second digestion of the emulsion, or the metal compounds can be added to the emulsion lust before coating the emulsion. The metal compounds are advantageously incorporated in the emulsion-s in the form of their solutions in a suitable solvent, e. g. water, methyl alcohol, ethyl alcohol, etc.

Sulfur sensitizers are advantageously also added to the emulsions. Gelatins normally contain certain sulfur compounds which act as sulfur sensitizers of photographic emulsions, but beneficial effects are obtained in accordance with our invention by adding sulfur sensitizers, i. e. sulfur compounds containing C=S groups or -S-S groups, e. g. t'hiourea, allyl isothiocyanate, thicsinamine, etc. Beneficia1 effects are also obtained by adding metal or ammonium thiocy-an'ates, e. g. sodium, potassium, ammonium, cadmium or calcium thiocyanates, to the emulsions. One or more sulfur sensitizer can be employed, and one or more thiocyanates selected from the group consisting of metal and ammonium thiocyanate's can be employed in conjunction with a sulfur sensitizer other than a thiocyanate containing a cation selected from the group consisting of metal and ammonium cations. The sulfur sensitizers are advantageously incorporated in the emulsion in the form of their solutions in a suitable solvent. such as water, methyl or ethyl alcohol.

The sulfur sensitizers can be incorporated in the emulsions at any stage of the preparation of the emulsion, e. g. during precipitation of the silver halides, during the first digestion (ripening) or during the second digestion of the emulsion. When incorporating thiocyanates in the emulsions prior to washing the amount can vary widely. Advantageously, however, an amount of thiocyanate equal to from about 2 to about 15 per cent by moles of the silver halide in the emulsion is employed. If the thiocyanate or other sulfur sensitizer is notadded until later in. the preparation, e. g. after washing, it is advantageous to employ an amount equal to from about 0.1 to about 2.5 per cent by moles of the silver halide present in the emulsion in the case of metal and ammonium thiocyanates, and an amount equal to from about 0.006 to about 0.06 percent by moles of the silver halide in the case of other sulfur sensitizers.

It is advantageous to digest, i. e. heat treat the emulsion with both the metal compound and the sulfur sensitizer present, at an appropriate temperature, e. g. at from 100 to 150 F. During digestion, i. e. the second digestion as contrasted with the first digestion or ripening, the pH of the emulsion is advantageously adjusted to the acid side of neutrality, e. g. between 5 and 7. Maintenance of the emulsion on the acid side of neutrality during coating is also advantageous.

The following examples will serve to illustrate further the manner of practicing our invention.

Example 1 A. A fast negative-type gelatino-silver-bromiodide emulsion having a silver halide content (principally silver bromide) of about 218 g. of silver halide per six liters of emulsion was prepared by precipitating the silver halides in an aqueous gelatin solution, adding 16 g. of sodium thiocyanate, for each 218 g. of silver halide, digesting (ripening) the resulting emulsion, adding gelatin to the ripened emulsion and dissolving the gelatin, setting the emulsion by chilling, washing the chilled shredded emulsion and melting-out and digesting the washed emulsion. The emulsion was then coated on a glass plate and dried in the usual manner.

B. The same type of emulsion as described under A above was prepared in the same manner as described under A above, except that 0.005 g. of (NH4)2PtCl4 per each 218 g. of silver halide were added to the emulsion at the beginning of the precipitation of the silver halides. After precipitation and digestion (ripening), further gelatin was added and dissolved, and the emulsion was set by chilling and washed, as under A. The emulsion was then melted down and digested at a pH of about 6.5. The emulsion was then coated on a glass plate and dried in. the usual manner.

C. The same type of emulsion as described under A above was prepared in the same manner as described under A above, except that, after the silver halide was precipitated, 0.01 g. of (NI-IQzPtCh and then 0.02 g. of ascorbic acid per each 218 g. of silver halide were added. The emulsion was then digested (ripened), further gelatin added and dissolved, and the emulsion was set by chilling and washed. The emulsion was melted down and digested at a pH of about 6.5. The emulsion was then coated on a glass plate and dried in the usual manner.

D. The same type of emulsion as described under A above was prepared in the same manner as described under A above, except that after the first digestion (ripening), 0.002 g. of (NH4)2PtCl4 and 0.004 g. of ascorbic acid per each 218 g. of silver halide were added. Further gelatin was added and dissolved, and the emulsion was set by chilling and washed. The emulsion was melted down and digested at a pH of about 6.5. The emulsion was then coated on a glass plate in the usual manner.

Each of the coated emulsions prepared as described above was exposed and developed for 8 minutes in Eastman Kodak Companys D-19 developer at 68 F. Results were as follows:

Coated Emulsion ggg gamma fog Example 2 acteristics:

white light speed (IO/i) gamma mg B. To another portion of the same emulsion were added 0.005 g. of (NH4)2PdCls and 0.044 g. of ascorbic acid per 218 g. of silver halide, after the emulsion was ready for coating. The emulsion was then allowed to stand at about 42, F. for 30 minutes and was then coated, exposed and developed as above, with the following results:

White light speed (lO/i) gamma fog C. With 0.01 g. of (NHmPdCle and 0.088 g, of ascorbic acid and proceeding as above, the following results were obtained:

white light speed (IO/i) gamma fog Ascorbic acid was employed in the foregoing examples as a reducing agent and the employment of a reducing agent in connection with the metal compounds is advantageous.

The thiocyanates which we have found are most advantageously employed in practicing our invention are the alkali metal thiocyanates, e. g. sodium or potassium thiocyanate, the alkaline earth metal thiocyanates, e. 9:. calcium thio' cyanate, and the ammonium thiocyanates, e. g. NH4SCN. Of course, =thiocyanates containing cations which cations are known to have, in themselves, a deleterious efiect on silver halide emulsions should be avoided. Otherwise the beneficial effects attained by our invention would be partially nullified by th deleterious action oi the cation. Thus, iron thiocyanate which con-; tains the iron cation should be avoided. I

sensitizing dyes of all types can be employed to spectrally (optically) sensitize our new emulsions, e. g. erythrosin, Congo red, any of the sensitiz ing cyanine dyes (monomethine, trimethine, pentamethine, heptamethine, etc.), any of the sensitizing merocyanine dyes (see United States Patent 2,078,233, dated April 27, 1937, for exam-g ple), any of the sensitizing hemicyanine dyes (see United States Patent 2,166,736, dated July 18; 1939, for example), any of the sensitizing hemi oxonol dyes (see United States Patent 2,216,441, dated October 1, 1940, and United States Patent 2,165,339, dated July 11, 1939, for example), etc.

Photographic elements comprising our new emulsions can be made up in the usual manner by coating the fiowable emulsions on to a support of a suitable material, such as glass, photographic paper, cellulose derivative or resin film, etc., to' desired thickness, and then setting the coated emulsion.

Our new emulsions can contain hardening agents, setting agents, stabilizing agents, supersensitizing combinations of sensitizing dyes or a supersensitizing combination of one or more sensitizing dyes and another substance. 5

In terms of liters of wet emulsion, the concen tration of metal compound advantageously em} ployed in practicing our invention is from about 0.002 to somewhat less than 0.01 g. per liter of wet emulsion, and advantageously from about 0.0002 to about 0.005 g. per liter of wet emulsion,

What we claim as our invention and desire to be secured by Letters Patent of the United States is: 1. In a process for preparing a sensitized photographic silver halide emulsion, the step which comprises digesting the emulsion, on the acid side of neutrality, in the presence of at least-one sulfur sensitizer and at least on soluble metal graphic gelatino-silver bromolodide emulsion, the.

step which comprises digesting the emulsion, on

the acid side of neutrality, in thepresence'of at least one sulfur sensitizer and at least one soluble metal compound, the metal being selected from the group consisting of metals; in group VIII of the periodic arrangementof the elements having.

an atomic weight greater than 100, the quantity of said. soluble metal compound being from. 0.8 to 39,4 milligrams per-each 100 grams of silver present in the emulsion.

4, In a process for preparing a sensitized photographic gelatino-silver-bromoiodide.emulsion, the

step which comprises digesting the-emulsion, on a the acid side of neutrality, in the presence .of at least one sulfur sensitize'r and at least onesoluble metal saltaselected from those represented by the following general formula: .RzMXs wherein R 7 consisting of a platinum atomand a palladium atom, and X represents a halogen atom selected from the group consisting of a chlorine atom and a bromine atom, the quantity of said soluble metal salt being from 0.8 to 39.4 milligrams per 1 each 100 grams of silver present in the emulsion.

5. In a process for preparing a sensitized photographic gelatino-silver-bromoiodide emulsion, the

, ep which comprises digesting the emulsion, on

compound, the metal being selected from the group consisting of metals in group VIII of the periodic arrangement of the elements having an atomic weight greater than 100, the quantity of said soluble metal compound being from 0.8 to 39.4 milligrams per each 100 grams of silver present in the emulsion.

2. In a process for preparing a sensitized photographic gelatino-silver-halide emulsion, the step which comprises digesting the emulsion, on the acid side of neutrality, in the presence of at least one sulfur sensitizer and at least one soluble metal compound, the metal being selected from the group consisting of metals in group VIII of the periodic arrangement of the elements having an atomic weight greater than 100, the quantity of said soluble metal compound being from 0.8 to 39.4 milligrams per each 100 grams of silver present in the emulsion.

3. In a process 'for preparing a sensitized photothe acid side of neutrality, in the presence of at least one thiocyanate selected from the group consisting of sodium, potassium, calcium, cadmium and ammonium thiocyanates, and at least one soluble metal salt selected from those represented by the following general formula: RzMXs wherein R represents a member selected from the group consisting of a hydrogen atom, a sodium atom, a potassium atom and an ammonium radical. M representsa metal atom selected from the group consisting of a platinum atom and a palladium atom, and X represents a halogen atom selected from the group-consisting of a chlorine atom and a bromin atom, the quantity of said soluble metal salt: being fr'om'0.8 to 39.4 milligrams per each 100 grams of silver present in the emulsion.

6. In a process for preparing a sensitized photographic gelatino-silver-bromoiodide emulsion, the step which comprises digesting the emulsion, on the acid side of neutrality, in the presence of sodium thiocyanate and ammonium chloropalladate having the following formula:

(NH4) zPdClo the quantity of the ammonium chloropalladate being from 0.8 to 39.4 milligrams per each 100 grams of silver present in the emulsion.

7. In a process for preparing a sensitized photol graphic gelatino-silver-bromoiodide emulsion, the

step which comprises digesting the emulsion; on the acid side of neutrality, in the presence of at least one thiocyanate selected from the group consisting of sodium, potassium, calcium, cadmium and ammonium thiocyanates, and at least one 7 a bromine atom, the quantity of said soluble metal salt being from 0.8 to 39.4 milligrams per each 100 grams of silver present in the emulsion.

8. In a process for preparing a sensitized photographic gelatino silver bromoiodide emulsion, the step which comprises digesting the emulsion, on the acid side of neutrality, in the presence of sodium thiocyanate and. ammonium chloroplatinite having the formula: (NHozPtCh, the quantity of the ammonium chloroplatinite being from 0.8 to 39.4 milligrams per each 100 grams of silver present in the emulsion,

9. In a process for preparing a sensitized photographic gelatino-silver-bromoiodide emulsion, the step which comprises digesting the emulsion, on the acid side of neutrality, in the presence of sodium thiocyanate, ascorbic acid and ammonium chloroplatinite having the formula:

(NH4) zPtCls the quantity Of the ammonium chloroplatinite being from 0.8 to 39.4 milligrams per each 100 grams of silver present in the emulsion.

10. In a process for preparing a sensitized photographic gelatino-silver-bromoiodide emulsion, the step which comprises digesting the emulsion, on the acid side of neutrality, in the presence of sodium thiocyanate, ascorbic acid and ammonium chloropalladate having the formula:

(NH4) zPdCls the quantity of the ammonium chloropalladate being from 0.8 to 39.4 milligrams per each 100 grams of silver present in the emulsion.

11. In a process for preparing a layer of a sensitized photographic silver halide mulsion, the step which comprises digesting a photographic silver halide emulsion, on the acid side of neutrality, in the presence of at least one sulfur sensitizer and at least one soluble metal compound, the metal being selected from the group consisting of metals in group VIII of the peroidic arrangement of the elements having an atomic weight greater than 100, the quantity of said soluble metal compound being from 0.8 to 39.4

8 milligrams per each 100 grams of silver present in the emulsion, and coating the so-digested emulsion upon a support while maintaining the emulsion on the acid side of neutrality.

12. In a process-for preparing a layer of a sensitized photographic gclatino-silver-halide emulsion, the step which comprises digesting a photographic gelatino-silver-halide emulsion, on the acid side of neutrality, in the presence of at least onesulfur sensitizer and at least one soluble metal compound, the metal being selected from the group consisting of metals in group VIII of the periodic arrangement of the elements having an atomic weight greater than 100, the quantity of said soluble metal compound being from 0.8 to 39.4 milligrams per each 100 grams of silver present; in the emulsion, and coating the so-digested emulsion upon a support while maintaining the emulsion on the acid side of neutrality.

13. The emulsion obtained by the process of claim 1.

14. The emulsion obtained by the process of claim 2.

15. The emulsion obtained by the process of claim 3.

16. The emulsion obtained by the process oi claim 4.

17. The emulsion obtained by the process of claim 5.

18. The emulsion layer obtained by the process of claim 11.

19. The emulsion layer obtained by the process of claim 12.

WILLIAM F. SMITH. ADRIAN P. H. TRIVELLI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

